Single-pion production in pp collisions at 0.95 GeV/c (II)

摘要

he single-pion production reactions pp ( ) dπ~+, pp( )npπ~+ and pp ( ) ppπ~0 were measured at a beam momentum of 0.95 GeV/c (T_p( )400 MeV) using the short version of the COSY-TOF spectrometer. The central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements from other detector parts. Thus all pion production channels were recorded with 1-4 overconstraints. The main emphasis is put on the presentation and discussion of the npπ~+ channel, since the results on the other channels have already been published previously. The total and differential cross-sections obtained are compared to theoretical calculations. In contrast to the ppπ~0 channel we observe in the npπ~+ channel a strong influence of the Δ excitation. In particular, the pion angular distribution exhibits a (3 cos~2 Θ+1)-dependence, typical for a pure s-channel excitation and identical to that observed in the dπ~+ channel. Since the latter is understood by a s-channel resonance in the ~1D_2 pn partial wave, we discuss an analogous scenario for the pnπ~+ channel.